Download Ch 27 Prokaryotes

CHAPTER 27
Prokaryotes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• They’re (Almost) Everywhere!
• Most prokaryotes are microscopic
– But what they lack in size they more than
make up for in numbers
• The number of prokaryotes in a single handful
of fertile soil
– Is greater than the number of people who have
ever lived
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• Prokaryotes thrive almost everywhere
– Including places too acidic, too salty, too cold,
or too hot for most other organisms
Figure 27.1
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• Structural, functional, and genetic adaptations
contribute to prokaryotic success
• Most prokaryotes are unicellular
– Although some species form colonies
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• Prokaryotic cells have a variety of shapes
– The three most common of which are spheres
(cocci), rods (bacilli), and spirals
1 m
Figure 27.2a–c (a) Spherical (cocci)
2 m
(b) Rod-shaped (bacilli)
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5 m
(c) Spiral
Cell-Surface Structures
• One of the most important features of nearly all
prokaryotic cells
– Is their cell wall, which maintains cell shape,
provides physical protection, and prevents the
cell from bursting in a hypotonic environment
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• Using a technique called the Gram stain
– Scientists can classify many bacterial species into
two groups based on cell wall composition, Grampositive and Gram-negative
Lipopolysaccharide
Cell wall
Peptidoglycan
layer
Cell wall
Outer
membrane
Peptidoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Grampositive
bacteria
Gramnegative
bacteria
20 m
(a) Gram-positive. Gram-positive bacteria have
a cell wall with a large amount of peptidoglycan
that traps the violet dye in the cytoplasm. The
alcohol rinse does not remove the violet dye,
which masks the added red dye.
Figure 27.3a, b
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(b) Gram-negative. Gram-negative bacteria have less
peptidoglycan, and it is located in a layer between the
plasma membrane and an outer membrane. The
violet dye is easily rinsed from the cytoplasm, and the
cell appears pink or red after the red dye is added.
• The cell wall of many prokaryotes
– Is covered by a capsule, a sticky
layer of polysaccharide or
protein
Capsule
• Some prokaryotes have fimbriae and
pili
– Which allow them to stick to their
substrate or other individuals in
a colony
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Fimbriae
Motility
• Most motile bacteria propel themselves by flagella
– Which are structurally and functionally different
from eukaryotic flagella
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Figure 27.6
Plasma
membrane
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• The typical prokaryotic genome
– Is a ring of DNA that is not surrounded by a
membrane and that is located in a nucleoid region
Chromosome
Figure 27.8
1 m
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• Prokaryotes reproduce quickly by binary fission
– And can divide every 1–3 hours
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• A great diversity of nutritional and metabolic
adaptations have evolved in prokaryotes
• Types of nutrition:
– Photoautotrophy: light + atmospheric CO2 = organic
compounds (cyanobacteria, plants, algae, protists)
– Chemoautotrophy: inorganic substances (ammonia,
sulfide) + atmospheric CO2 = organic compounds.
– Photoheterotrophy: light for energy and carbon in organic
form (marine prokaryotes)
– Chemoheterotrophy: consume organic compounds for
both energy and carbon (decomposers)
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• Major nutritional modes in prokaryotes
Table 27.1
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Metabolic Relationships to Oxygen
• Prokaryotic metabolism
– Obligate aerobes
• Require oxygen
– Facultative anaerobes
• Can survive with or without oxygen
– Obligate anaerobes
• Are poisoned by oxygen
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Lessons from Molecular Systematics
•
Molecular systematics
–
Is leading to a phylogenetic classification of prokaryotes
–
2 clades of prokaryotes: bacteria and archaea
Domain
Archaea
Domain Bacteria
Proteobacteria
Universal ancestor
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Domain
Eukarya
Bacteria
• Diverse nutritional types
– Are scattered among the major groups of
bacteria
• The two largest groups are
– The proteobacteria and the Gram-positive
bacteria
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Archaea
• Archaea share certain traits with bacteria
- And other traits
with eukaryotes
- Have many unique
characteristics
Table 27.2
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Archaea
• Live in extreme environments
–
Extreme thermophiles
• Thrive in very hot environments
–
Extreme halophiles
• Live in high saline environments
–
Methanogens
• Live in swamps and marshes
• Produce methane as a waste product
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Roles of prokaryotes
• Prokaryotes play crucial roles in the biosphere
• Prokaryotes are so important to the biosphere
that if they were to disappear
– The prospects for any other life surviving
would be dim
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• Chemoheterotrophic prokaryotes function as decomposers
– Breaking down corpses, dead vegetation, and waste
products
– Recycling of chemical elements between the living and
nonliving components of the environment in
ecosystems
• Nitrogen-fixing prokaryotes
– Add usable nitrogen to the environment
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Symbiotic Relationships
• Many prokaryotes
– Live with other organisms in symbiotic
relationships such as mutualism and
commensalism
Figure 27.15
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• Other types of prokaryotes
– Live inside hosts as parasites
• Prokaryotes have both harmful and beneficial
impacts on humans
• Some prokaryotes are human pathogens
– But many others have positive interactions with
humans
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Pathogenic Prokaryotes
• Prokaryotes cause about half of all human
diseases
– Lyme disease is an example
Figure 27.16
5 µm
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Prokaryotes in Research and Technology
• Experiments using prokaryotes
– Have led to important advances in DNA
technology
• Prokaryotes are also major tools in
– Mining
– The synthesis of vitamins
– Production of antibiotics, hormones, and other
products
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings